Can't find your keys ... again? Whether your momentary memory loss is linked to doing too many things at once or just a bad case of menopausal brain fog, you don't have to put up with it.

Research suggests exercise even once a week may help you maintain cognitive function as you age.

In fact, experts say you can instantly boost your chances of remembering where you put your keys--and everything else you keep forgetting--if you start treating your brain right (no matter your age). Our simple lifestyle changes will help you stay sharp as the years go by.

The 30s

Floss every day: What do loving licorice and hating the idea of flossing have in common? Both can contribute to plaque on your teeth, which is surprisingly bad for your brain. "The plaque between teeth can cause an immune reaction that attacks arteries, which then can't deliver vital nutrients to brain cells," says Dr. Michael Roizen, co-author of "YOU--The Owner's Manual: An Insider's Guide to the Body that Will Make You Healthier and Younger." Solution? Floss every day. Can't remember? Keep the floss where you store your morning makeup.

Multitask at the gym: Just as working out can keep your body in good shape as you age, stretching your brain can keep it in top form, too. And doing them together is double the fun: Do a crossword puzzle while riding a stationary bike or listen to language lessons on your iPod while running. Scientists say that working the body and mind at the same time revitalizes brain cells. Don't like multitasking? Hit the crossword right after the gym, when your brain is energized.

Go fish: Look to the sea for healthy ways to feed your brain. DHA, a type of omega-3 fatty acid found in salmon, trout, and some fortified foods such as yogurt, is a super saver for your memory. Health.com: How yoga can help you remember

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"DHA decreases arterial inflammation and improves repair of the protective sheath around nerves," Roizen says. "The result is less age-related memory loss, less Alzheimer's disease, less depression, and a quicker mind."

The 40s

Steal your kids' toys: There's a new version of that Rubik's Cube that you loved as kid. It's the 3-D-like Rubik's 360, and it's probably good for brains of any age, because it sharpens flexible problem-solving skills, says neuropsychologist Karen Spangenberg Postal, Ph.D., president of the Massachusetts Psychological Association.

The key: As you play, you're working on your memory, strategy, and spatial skills--all required for improving brain health--at the same time. What if you always found the Cube endlessly frustrating? No worries: Any game that stretches your thinking is helpful. Health.com: Why you can't concentrate

Just do it: Elevating your heart rate three times a week for 20 minutes--even just by walking--bathes your brain in oxygen and helps it grow new cells.

"Aerobic exercise is two to three times as effective as any known brain-training activity," says Sam Wang, Ph.D., associate professor of neuroscience at Princeton University and co-author of "Welcome to Your Brain: Why You Lose Your Car Keys but Never Forget How to Drive and Other Puzzles of Everyday Life."

If you have no time for the gym during the week, that's OK: Recent research shows moderate to vigorous exercise even just once a week (say, a weekend jog) makes you 30 percent more likely to maintain your cognitive function as you age.

Start a bridge club: If book clubs bore you and dinner parties leave you exhausted, then maybe a brisk game of bridge is just what the doctor ordered. The combination of strategy and memory in bridge challenges the brain to learn new information and exercises cells so they don't die, Postal says. Health.com: How to pick the right supplement

Plus, socializing while playing cards adds a level of unpredictability that gives your brain a charge--something solo games don't offer. Bridge is definitely on the comeback, so you can learn to play through a community college or continuing education program, or hire a private instructor for lessons.

The 50s Plus

Use chopsticks: "Studies show that engaging the concentrated areas of nerve cells in your fingertips directly stimulates your brain," says Maoshing Ni, Ph.D., author of "Second Spring: Dr. Mao's Hundreds of Natural Secrets for Women to Revitalize and Regenerate at Any Age." Truth is, any fingertip activity--using chopsticks, knitting, or even rolling a pen or pencil between your fingers--also helps your brain by boosting your circulation. And good circulation helps eliminate waste products that can prevent nutrients from reaching your brain.

Play electronic games: No, you're not too old for a Wii or one of the new handheld brain-exercise games. And it may even be good for you, since simply trying something new gets your brain juiced, says neuropsychologist Reon Baird, Ph.D., of the Long Beach Memorial Medical Center. Health.com: More tricks to improve your memory

"When that something new is a video game, you'll stimulate different parts of the brain that you don't normally use on a day-to-day basis," she says. Try "Brain Challenge" for the Wii or "Brain Age" for the Nintendo DS. If that's too techy for you, play along with "Wheel of Fortune" or "Jeopardy!" on TV, Baird says. Challenge your know-it-all spouse to make it more fun.

Be careful with meds: If you ache every time you work out and never sleep well due to night sweats, there's a pill for that. But be careful: Research in Clinical Interventions in Aging reveals that nonprescription sleep aids may cause some "cognitive impairment"--like confusion-- in older adults. How much is unknown, but you're probably familiar with the next-day grogginess. And the medicine known as diphenhydramine (found in many allergy medications and nighttime pain pills) has an "anticholinergic" effect; it blocks communication between nerve cells. Talk with your doctor about other remedies like relaxation or cognitive therapy for sleep problems.